I am working on a project and struggle a bit with a subject about melatonin.

I know already a lot about sleeping and the fact that melatonin helps a lot of people to sleep.
But in mice melatonin levels are also high during night, however they are awake then. And when mice have a defect in melatonin production their sleep/circadian rhythm is abberant.
I wondered how this can be explained... Does anyone have any suggestions? I already read a lot of articles, all saying that melatonin is higher when mice are awake, but not explaining this difference.

I was thinking of different receptors (MT1/2) to be activated, resulting in a different response in mice compared to human. However, mice are often used as model organism to test clinical applicability of melatonin.

If anyone has something to help me, please let me know, even if these are only thoughts!